On Jan 17, 8:20*am, "David Looser"
wrote:
"Andy Evans" wrote in message

No virtue in batteries, and a pig to implement. I have tried, but a
good current source sounds just as good as long as you can get the hum
right down.

Heavy filamented DHTs were comonly run from raw AC in the old days so I
don't know why you think you need to keep the hum "right down". Valve
filaments should really be supplied from a voltage, rather than a current,
source. The only advantage of feeding them with a current source is that it
reduces the switch-on surge, but again with heavy filaments that really
isn't an issue.

David.

Quite. I wrote a long screed on this subject and then trashed it as
counterproductive to Andy's purpose. The ultrafidelista generally use
AC fils because they sound best, and if they want to regulate the
plate voltage, use a constant current loaded shunt regulator made with
a bigger tube next to each power tube. But Andy's on a learning curve,
and he won't know that all this regulation is a bridge too far -- I
mean the danger of creating an over-refined tube amp that sounds just
like a silicon amp but more expensive so -- until he hears it and
starts backing off to where he likes the sound. You gotta do it for
yourself; that's part of the fun.

Andre Jute
Arrival is merely the start of the next journey